Coating compositions with a variety of different chemical and physical properties are known. Different areas of ultimate use may require either drastic or subtle differences in these properties.
In the lithographic printing plate technology, photoreactive compositions are sought which have desirable properties and which are substantially different before and after they are reacted. For example, when a photoreactive composition is on a light sensitive lithographic plate, it should be stable (i.e., not subject to separation of diverse components), resistant to mild contact (i.e., not tacky so as to prevent loss of composition when the reactive surface contacts other materials), and storage stable (i.e., not change its reactivity by losing components through evaporation), yet also being capable of fast curing and easy development (i.e., removed) by solvents when not cured. The cured composition must on the other hand be tough, resistant to solvents, and oleophilic. These are difficult properties to combine in the compositions which are required in the lithographic printing art. Where extreme properties are required, such as sufficient strength and durability in the cured film to provide accurate copies on press for in excess of half a million copies, the difficulty in finding compositions which meet these requirements is multiplied.
In the lithographic printing art, the standard for high quality, long run printing plates is the bimetallic printing plate. This plate is composed entirely of metal to provide a longlasting printing plate. The most significant problem with the plate is that it cannot be formed quickly by exposure and wash development, but must rather be prepared by a much slower and expensive etching process.
It is a consideration of the present invention to provide a photoreactive, developable composition for use on printing plates to provide plates having press lives which approach that of bimetallic plates.